The network, which several years ago rejected some left-leaning issue advertisements, acknowledges that it has changed its policy.

A large Super Bowl display is located on the beach in Fort Lauderdale, Fla.… (J. Pat Carter / Associated…)

CBS Corp., acknowledging Tuesday that it has changed its policy and now accepts commercials that advocate political causes, defended its decision to run a politically sensitive advertisement during next month's Super Bowl.

The thicket that CBS finds itself in could become increasingly common for TV networks and local stations. Last week the U.S. Supreme Court lifted a decades-old prohibition that prevented corporations from buying ads and financing candidates and campaigns. Now media analysts are predicting that as much as $500 million in corporate money could flood this year's political campaigns, unleashing a torrent of issue advertising that will force TV executives to weigh the ever-shifting debate about which commercials cross the line.

The CBS Super Bowl commercial, sponsored by the evangelical Christian group Focus on the Family, features University of Florida football star Tim Tebow and his missionary mother, Pam, discussing her decision 23 years ago to continue with her pregnancy despite complications. She was pregnant with her son, winner of the 2007 Heisman Trophy.

Focus on the Family, based in Colorado Springs, Colo., and founded by James Dobson, described its first Super Bowl advertisement as a celebration of "family and life [and] comes at the right moment in the culture, because families need to be inspired."

CBS' decision on the Tebow ad comes as networks and TV stations have struggled for revenue amid a weak advertising market. Until recently, networks were routinely able to command higher rates each year for Super Bowl commercials, but that ended with the recession. CBS has been selling 30-second spots in the Feb. 7 Super Bowl for about $2.7 million each -- slightly less than NBC was able to command for last year's game -- and still has some advertising time left to sell.

A CBS spokesman said the Tebow commercial was subjected to the "full standards process that all ads go through" and accepted only after the script was reviewed.

The network nonetheless finds itself in a difficult position because, several years ago, CBS rejected ads -- some intended for the Super Bowl -- from left-leaning organizations, including MoveOn.org, People for the Ethical Treatment of Animals and the United Church of Christ, which advocates gay rights.

CBS' shift in policy has galvanized a coalition of organizations, which have been urging the network to reject the Tebow ad on the grounds that it offends Americans who believe that "reproductive decisions should be left to a woman and her physician."

"CBS has had a well-documented position that it would not accept ads about contentious or controversial subjects," said Jehmu Greene, president of the New York-based Women's Media Center, which is spearheading the campaign. "I don't think there is another issue in our society as contentious and controversial as abortion. There is some very strong hypocrisy at work."

Seeking to clarify its position, CBS released a statement Tuesday that said most other media outlets accepted issue advertisements.

"We have for some time moderated our approach to advocacy submissions after it became apparent that our stance did not reflect public sentiment or industry norms on the issue," CBS said.

But if advocates on either side of the debate were hoping CBS would reverse its policy shift, they are probably out of luck. The network said it would "continue to consider responsibly produced ads from all groups for the few remaining spots in Super Bowl XLIV."

When CBS rejected issue advertisements by liberal groups, George W. Bush was president and a majority of the Federal Communications Commission members were Republicans. Moreover, the network already had had a painful run-in with regulators after it was slapped with stiff fines because Janet Jackson's breast was briefly exposed during the 2004 Super Bowl halftime show.

Critics of CBS' policy shift said the network succumbed to financial pressures.

"They are more concerned about their bottom line than fair play," Greene said.

For last year's Super Bowl, an NBC station rejected an antiabortion ad that contained images of a fetus. NBC also rejected a commercial from PETA because it showed women handling vegetables in sexually suggestive ways. Greene said CBS should follow suit.

Her nonprofit group has been joined by others, including the National Organization for Women, Physicians for Reproductive Choice and Health, and the California Council of Churches Impact.

The groups' lobbying of CBS prompted others to voice support of the network's decision.

"I can understand why CBS might not want to offend viewers by using its airwaves for a hard-core, pro-life, antiabortion ad that might be upsetting to people. But this is not that kind of an ad," said Brent Bozell, president of the conservative watchdog organization Media Research Center.

He said other CBS actions -- including accepting Go Daddy ads, which typically feature big-breasted women, or broadcasting the Victoria's Secret runway fashion show -- were more objectionable.

"That offends a whole lot more women than this advertisement will," Bozell said. "The last thing that CBS should do is buckle under the pressure of this pressure group."